A liquid crystal display device that carries out an AC driving such as a gate line reverse driving in which polarities of display data in an identical line are identical to each other has an advantage of increasing a liquid crystal applied voltage while narrowing a data signal electric potential range, by individually driving storage capacitor wirings provided in respective lines.
FIG. 6 shows an example of an equivalent circuit of a picture element PIX included in such a liquid crystal display device for driving the storage capacitor wirings.
The picture element PIX includes a TFT 101 that serves as a selection element of the picture element PIX, a liquid crystal capacitor CL, and a storage capacitor Cs. A gate, a source, and a drain of the TFT 101 are connected to a gate line GL, a source line SL, and a picture element electrode 102, respectively. The liquid crystal capacitor CL is defined by the picture electrode 102, a common electrode COM, and a liquid crystal layer provided between the picture element electrode 102 and the common electrode COM. The storage capacitor Cs is defined by the picture element 102, a storage capacitor wiring CSL, and an insulating film provided between the picture element electrode 102 and the storage capacitor wiring CSL. A common electric potential Vcom is applied to the common electrode COM, and a storage capacitor electric potential Vcs of High level or Low level is applied to the storage capacitor wiring CSL. The picture element PIX includes a parasitic capacitor such as a parasitic capacitor Cgd formed between the picture element electrode 102 and a scanning signal line GL (the gate line GL).
In the picture element PIX, a data signal electric potential is written in the picture element electrode 102 while the TFT 101 is being active, and then the TFT 101 is made inactive. Thereafter, the storage capacitor electric potential Vcs to be applied to the storage capacitor wiring CSL allocated to the picture element PIX is changed from Low level to High level. This causes a picture element electrode electric potential Vdr to be raised from V+ to V+′ via the storage capacitor Cs, as shown in FIG. 7. Accordingly, a liquid crystal applied voltage VLC+ having a sufficiently great positive polarity can be obtained even in a case where a supplied data signal electric potential for display of positive polarity is low, provided that the common electric potential Vcom, the storage capacitor Cs and the storage capacitor electric potential Vcs are set such that the picture element electrode electric potential Vdr that has become V+′ by a raise of ΔV+ moves away from the common electric electrode Vcom toward a positive direction. Note that the V+ is determined in accordance with a gray scale level, and should not necessarily be lower than the common electric potential Vcom.
Further, in a case where (i) the data signal electric potential is written in the picture element electrode 102, (ii) the TFT 101 is made inactive and then (iii) the storage capacitor electric potential Vcs is changed from High level to Low level, the picture element electrode electric potential Vdr is decreased from V− to V−′ via the storage capacitor Cs. Accordingly, a liquid crystal applied voltage VLC− having a sufficiently great negative polarity can be obtained even in a case where a supplied data signal electric potential for display of negative polarity is great, provided that the storage capacitor Cs and the storage capacitor electric potential Vcs are set such that the picture element electrode electric potential Vdr that becomes V−′ by a decrease of ΔV− moves away from the common electric potential Vcom toward a negative direction. Note that the V− is determined in accordance with a gray scale level, and should not necessarily be greater than the common electric potential Vcom.
It is accordingly possible to further narrow a whole data signal electric potential range Vrange including a range of a data signal electric potential for display of positive polarity and a range of a data signal electric potential for display of negative polarity than a case where the picture element electrode electric potential Vdr obtained by writing, in the picture element PIX, the data signal electric potential for display of positive polarity and the data signal electric potential for display of negative polarity that are distributed via the common electric potential Vcom is used as it is. This makes it possible to reduce a power supply voltage that generates a gray scale reference voltage, thereby attaining low power consumption of the liquid crystal display device and driving of the liquid crystal display device at a high frequency.